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UK RNI for vitamin C: 40 mg/day (SACN); most UK adults achieve this through diet. EFSA-authorised claims: immune function, collagen synthesis, iron absorption enhancement, protection from oxidative stress. Megadose vitamin C supplementation (1,000 mg+) has no RCT evidence for preventing colds in the general population (Hemilä 2013 Cochrane review). Smokers have genuinely higher needs (~80 mg/day). Food sources provide vitamin C with additional phytonutrients that supplements cannot replicate.